1. Field of the Invention
The present invention relates to electronic components, and in particular to an improvement in structure in relation to an external electrode formed on an electronic component body.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a monolithic ceramic capacitor 1 as an exemplary conventional electronic component which is of interest in the present invention.
The monolithic ceramic capacitor 1 is provided with a chip capacitor body 2 as an electronic component body, and thick external electrodes 3 are formed at two opposing ends of the capacitor body 2. In the formation of the external electrodes 3, a paste containing a metal such as copper or silver as a conductive component is applied to predetermined positions of the capacitor body 2 and then is baked. In the interior of the capacitor body 2, a plurality of internal electrodes 4 arc layered and each of the internal electrodes 4 is electrically connected to one of the external electrodes 3.
A barrier layer 5 composed of nickel is formed on each external electrode 3, and then an outer layer 6 composed of tin or solder is formed on the barrier layer 5.
If the barrier layer 5 is not formed, undesirable solid-phase diffusion will occur between the external electrode 3 and the solder used for soldering the monolithic ceramic capacitor 1 onto a circuit board (not shown in the drawing) or between the external electrode 3 and the external layer 6 when the monolithic ceramic capacitor 1 is used at high temperatures. In addition, liquid-phase diffusion also may occur when the solder is in a melted state. The barrier layer 5 prevents the solid-phase diffusion. The outer layer 6 is to improve solderability when the external electrode 3 is soldered to a predetermined conductive land on the circuit board.
In such a monolithic ceramic capacitor 1, however, the formation of the barrier layer 5 will cause other problems in some cases, as described below.
The barrier layer 5 is generally formed by wet plating. Thus, the capacitor body 2 provided with the external electrodes 3 must be dipped into a plating solution for the formation of the barrier layer 5. This will result in reduction of the ceramic component of the capacitor body 2, decrease in strength, deterioration of electrical characteristics or, in the worst case, interlayer separation due to penetration of the plating solution into the internal electrodes 4.
Also, the outer layer 6 is generally formed by wet plating and the plating solution in this case will also result in similar problems. Regarding this, it is known that a plating solution used in plating of tin noticeably results in the above problems.
A means is desired to avoid solid-phase diffusion in the external electrodes 3 without the formation of the barrier layer 5, which requires plating.